sorry to bump this old thread, but I'd like to update MESS to properly emulate these Namco boards too and I'd like to have a few confirmations
Namcot 175:
- can map only CHR-ROM to PPU RAM by writing at $8000-$bfff
- no mirroring control
- WRAM protect bit at $c000-$c7ff
- no additional sound
Namcot 340:
- can map only CHR-ROM to PPU RAM by writing at $8000-$bfff
- mirroring control to map CIRAM to PPU nametable at $e000-$e7ff
- no WRAM in any known cart (so unclear if there is any enable bit)
- no additional sound
Namcot 129/163
- can map either CHR-ROM or CIRAM to PPU RAM by writing at $8000-$bfff
- mirroring control to map either CIRAM or CHR-ROM to PPU nametable at $c000-$dfff
- WRAM protect bits at $f800-$ffff
- additional sound
is the above correct?
If so, I'd have a couple of questions about Namcot-163.
1. is there any game which actually uses CIRAM as PPU RAM?
I'd like to have a test case to see if I'm emulating it correctly
2. docs are not 100% clear about $f800 reg. it seems to work both as External RAM protect *and* for sound address... but when is it used for one and when for the other? does the effect depend on bit4 or on something else? or is it always used for both?
at the moment, I won't emulate the sound capabilities (I'm not really a sound guy, so I'll ask help to some other MAMEdev for that), but I'd like to have CIRAM and WRAM correct before that
thanks
EDIT: replaced spurious occurrence of CHR-RAM with CHR-ROM...